Two women who won a helicopter tour of Washington in a raffle were injured along with their pilot yesterday when the helicopter's engine failed and the craft plunged into the Tidal Basin.

The helicopter, which took off from a condominium development in Arlington, had reached the Jefferson Memorial shortly after 5 p.m. when the engine sputtered and the pilot began to circle about, looking for an emergency landing site.

After the engine misfired again, according to a witness, the stricken copter swooped out over the basin and suddenly plummeted toward the water, nose first.

The most severely injured of the occupants of the privately owned Hughes 300 helicopter was flown to the MedStar unit of the Washington Hospital Center by a U.S. Park Police helicopter.

The woman, identified as Joan Bullard, 24, of 4605 S. 28th Rd., Arlington, was listed last night in serious but stable condition, with back injuries.

Bullard, Margaret Snyder, her fellow passenger, and pilot Phuong Hollynh, were waist deep in water, standing on the submerged fuselage of the helicopter, when rescuers arrived.

Only a single blade of the helicopter's rotor showed above the water.

According to early accounts, Bullard and Snyder, a Justice Department lawyer who also lives in South Arlington, won the ill-fated helicopter ride at a raffle held during a promotional event at a condominium development in their neighborhood.

Owned by HASCO, a Montgomery County firm, the three-passenger helicopter rents for about $145 an hour. A number of people watched it lift off from Arlington as dark clouds began moving into the skies over the area.

After a time, some of those who say the liftoff became concerned and telephoned Arlington police to find out why the helicopter had not returned.

Near the Tidal Basin, amid Washington's monuments, U.S. Park Police officer Ken Donovan saw the helicopter circling overhead, flying lower than is normal.

It looked to Donovan as if the pilot was searching for an emergency landing site.

Donovan heard the craft's engine cough to a stop, then sputter to life. He noted little nearby open space that was clear of people.

The helicopter's engine misfired again, Donovan said, and suddenly the craft was heading into the water, tail in the air.

Ray Scheren was working inside the Tidal Basin boat center. The threatening weather had confined all the center's pedal boats to dock. "Hey," Scheren heard somebody say, "that helicopter went down."

Scheren and two othr employes of the center, Chris Lewton and Mike Gray, got into motorboats and sped to the scene on the southwest side of the basin, about 30 yards from shore.

"She's hurt her back," said the pilot, a South Vietnamese air force veteran, referring to Bullard, the most seriously injured.

The boat center employes supplied life preservers, helped ferry a Park Police officer to the scene, where the water was estimated to be about 10 to 15 feet deep, and watched for the arrival of the fire department rescue squad.

Using boats, backboards and a special litter for fracture patients, fire department rescue squad members helped bring the three injured to shore, as dozens of spectators watched intently.

Witnesses recalled that the occupants of the helicopter said little.

"They were just glad to be alive I guess," said Sgt. Dolph Biggs, of Engine 13, who was among the firefighters sent to the basin.

Snyder and Hollynh, the pilot, were taken to George Washington University hospital where both were reported in good condition with fractures of the back.

The cause for the reported engine problems could not be learned immediately.

The Federal Aviation Administration has begun an investigation.